[llvm] Reland "[LV]: Teach LV to recursively (de)interleave." (PR #125094)

[David Sherwood via llvm-commits]

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david-arm wrote:

Oh I think I understand. With just the first commit `@test_masked_interleave` crashes due to the mismatched cost model, which means you can't update the test in the first commit. The second commit works around the difference in cost model, which means we can successfully vectorize the test.

https://github.com/llvm/llvm-project/pull/125094